In a display ensemble comprising multiple color display apparatus, wherein a color display apparatus, also referred to as a color display or a display, comprises a color display device and a set of R, G and B Gamma one-dimensional look-up tables (1D LUTs), it may be desirable to calibrate all of the color displays to the same gray-scale chromaticity values, tone response function, also referred to as gamma curve, and maximum luminance value in order to assure consistent image appearance across display boundaries. Without calibration, when the same Red-Green-Blue (RGB) signals are sent to different color displays, even of the same make and model, each color display will, generally, produce different output colors, thereby making display boundaries noticeable and visually displeasing.
An RGB input signal received by a color display apparatus may be modified according to the RGB Gamma 1D LUTs, and the modified signals may be used to drive the color display device. The Gamma 1D LUTs may be used to set the proportions of maximum R, G and B signals, actually sent to the color display device, to achieve the desired displayed luminance and chromaticity at the white point. In addition, the Gamma 1D LUTs may be used to set the R, G and B signal levels, actually sent to the color display device, along the gray scale to control the chromaticity and tone response produced for gray, also considered equi-RGB, signals received by the color display apparatus.
A model of a response function, of a color display device, that predicts the color output, in CIE XYZ, from an input RGB signal may be required to properly generate the data for the RGB Gamma 1D LUTs. A model of the display device response function may be obtained by measuring the colors actually displayed, on the display device, in response to a variety of different RGB signal inputs, presented to the display device, and inverting the measured relationship between the displayed colors and the RGB signal inputs. The model of an individual display device may be used to generate the data for that display's RGB Gamma 1D LUTs, which may be used to modify that display's input RGB signals to achieve the desired chromaticity along the gray scale, the desired tone response function and the desired maximum luminance. By loading appropriate data into each display's Gamma 1D LUTs, the gray scale chromaticity, tone response function and maximum luminance may be made the same for all the displays, provided the desired chromaticity and maximum luminance are achievable on each display.
A color-measurement device, for example, a colorimeter or a spectroradiometer, may be used to measure a display's color outputs. A more accurate calibration may require more measurements with different RGB input signals, especially around the gray scale, making more accurate calibrations more time consuming and hence, more costly. Methods, systems and apparatus for generating an accurate calibration, with a small number of color measurements made of the display using a color-measurement device, may be desirable.